Preparation of chrome-tanned leather for dyeing



Patented June 4, 1929.

UNITED STATES PATENT OFFICE.

ROBERT HOWSON PICKARD, DOROTHY JORDAN LLOYD, AND ALBERT EDWARD lGAUNGE, OF LONDON, ENGLAND, ASSIGNORS T0 ROHM & HAAS COMPANY, OF

PHILADELPHIA, PENNSYLVANIA.

PREPARATION OF CHROME-TANNED LEATHER FOR DYEING.

No Drawing. Application filed August 22, 1925, Serial No.

This invention hasreference to improvements in and relating to the preparation-of chrome-tanned leather for storage in the crust condition previous to dyeing.

For some years it has been fashionable for ladies to wear shoes of a colour to match their dresses and as a consequence leather manufacturers have had to produce leathers of almost innumerable colours and shades of colours.

If vegetable tanned leather is required the problem is not difficult because such leather can be wet back from the crust state.

A demand has, however, for a long time existed for chrome leather dyed as aforesaid and hereupon certain practical difficulties arise which may briefly be described as follows:

It is not practicable to store chrome leather in the wet condition and if the leather is allowed to dry out by evaporation of its water content, one of the serious defects it possesses is that it cannot be dyed satisfactorily.

Leather manufacturers have therefore been compelled to dye the chrome leather by steeping this whilst in the wet blue condition in the dye solution, the dyed leather being thereafter air dried.

This, however, introduces another and very serious disadvantage in that they must maintain a large stock of dyed chrome leather in the hope that they may be able at short notice to supply leather of the percise colour and shade of colour that may be from time to time called for.

This obviously entails heavy capital outlay and it necessitates vastly increased storage accommodation and expenses incidental thereto. Further, there is often an accumulation of old stock which is usually disposed of at a loss because leather of the particular shade of colour to which it has been dyed is not called for in the ordinary course of their trade.

Manufacturers of chrome leather have therefore all along been at a serious disadvantage as compared with manufacturers of vegetable tanned leather.

The aforementioned disadvantage is obviated by our invention.

As a result of many experiments we find that acetone (preferably free from its homologues) possesses a peculiar and heretofore unsuspected characteristic in that if the de hydration of chrome leather is effected by ii the leather, after the acetone is removed, is

51,876, and in Great Britain August 27, 1924.

in a condition to be wet back in water-even after storage in crust condition for a very long t1meand therefore in a condition to be perfectly evenly dyed either at once or subin aposition of equality with manufacturers of vegetable tanned leather in that they need only keep a compartively small stock of chrome leather in the crust condition and from this supply the demand of dyed chrome leather as it arises.

The treatment'is best carriedout'by steeping the chrome leather in the wet blue and preferably in neutralized condition in a bath or in successive baths of acetone or by spraying with acetone and after drainin the acetone in the leather is evaporated 0% by sub- ]ecting it to the action of air or inert gas (both hereinafter included in the term gas) preferably warmed to 135 Fah. (57. cent.)

The acetone in the bath or at any rate that in the final bath will preferably be of full strength and the period of immersion will of course depend upon the thickness of the leather and also upon its character.

It is not therefore possible to give precise instructions as to the exact len th of time the leather should be immersed, %ut if sufficient acetone be used and the immersion be maintained until the leather is in equilibrium with a water and acetone mixture of specific gravity not reater than 0.810, it will suflice.

A very sa e test is to remove a sample cutting and dry this at 135 F., (57 cent.). If this wets back at once in water the treatment is complete and the excess of acetone may be at once drained off and the acetone content of the leather evaporated ofi as aforesaid.

The process can be carried out in any suitable type of continuous extraction plant designed to use economically such a volatile solvent as acetone.

Of course the evaporation of the acetone content of the leather will in practice be carried out so that the acetone is recovered and may again be used.

Claims: 1. A process for preparing chrome tanned leather for dyelng which Consists in steeping it whilst in the wet blue state in a' bath of ime eae ing it whilst a the wet biue state in a bath of acetone until the leather is in equilibrium with a water and acetone mixture'of specific gravity not greater than 0.810, and, after drainmg, evaporating oil the acetone by sub-v 15 jecting it to the action of gas.

ROBERT HOWSON PIOKARD. DOROTHY JORDAN LLOYD. ALBERT EDWARD 'GAUNGE. 

